1. Field of the invention
This invention relates to a novel information processing device and an information processing method which perform recording or erasing of information by voltage application and perform reproduction of information by detecting an evanescent wave.
Also, the present invention relates to an information processing device and an information processing method which is improved in S/N ratio in reproduction of information which is performed by detecting an evanescent wave.
2. Related Background Art
In recent years, uses of memory materials constitute the nuclei of electronics industries such as computers and their related instruments, video discs, digital audiodiscs, etc., and the developments of such materials have been extremely actively progressed. The performances demanded for memory materials, which depend on the uses, may include generally:
(1) high density and large recording capacity; PA1 (2) rapid response speed of recording and reproduction; PA1 (3) small power consumption; PA1 (4) high productivity and low cost, etc.
These materials have been heretofore primarily semiconductor memories or magnetic memories by use magnetic materials or semiconductors as the base material, but with the progress of the laser technique in recent years, an inexpensive and high density recording medium with an optical memory by use of an organic thin film such as an organic dye, a photopolymer, etc. has been developed.
On the other hand, the scanning tunneling microscopy (hereinafter abbreviated as STM) that can observe directly the electron structure of surface atoms/molecules of a conductor with a resolving power of 0.1 nm has been developed [G. Binning et al., Phys. Rev. Lett. 49, 57 (1982)]. There has been made a proposal concerning a recording-reproduction device which performs writing-reading onto a recording medium with a bit size of atomic/molecular order (0.5 to 50 nm) by use of the tunnel current applying the principle of STM [for example, Japanese Patent Application Laid-Open Nos. 63-161552 and 63-161553].
Also, as further development of STM, there have been developed a near field scanning optical microscope (NFOM) which examines the surface state of a sample by utilizing the evanescent wave oozed out from a fine opening smaller than the wavelength of the light at the pointed tip end of a probe to which light introduced from the opposite direction [Durig et al., J. Appl. Phys., 59, 3318 (1986)] or the photon scanning tunneling microscopy (PSTM) that permits light to enter from the back surface of a sample through a prism under the condition of total reflection, and detecting the evanescent wave oozed out to the sample surface [Reddick et al., Phys. Rev. B39, 767 (1989)]. By applying the principle of NFOM and utilizing an evanescent wave, there has been made a proposal concerning a recording-reproduction device which performs writing onto a recording medium and reading therefrom [U.S. Pat. No. 4,684,206].
However, of those which have been practically applied in the above prior art examples, even in the optical memory with the highest density and the largest recording capacity, the limit of recording capacity is 10.sup.8 bit/cm.sup.2, which is becoming no longer sufficient for image recording in computers or video instruments in recent years, etc.
In an attempt which performs recording and reproduction by accessing to one molecule, although the bit size of recording may be on an atomic/molecular order (0.5 to 50 nm), in such recording wherein a part of the structure within the molecular order changes, the influence of the recorded state on the tunnel current is local, whereby reproduction can be done with difficulty. Further, since there is also the possibility to change the recorded state by the operation of reproduction, it can hardly be said as being sufficiently applicable to a memory.
Also, in the attempt of recording and reproduction by use of NFOM as described above, the evanescent wave was weak in intensity for performing stable writing of information, and if the optical intensity is made stronger, there has been involved the problem that the bit diameter becomes larger.
If both recording and reproduction are performed by use of the evanescent wave, there also has been the problem that the written state is changed by the reproduction light.
Further, in reproduction of an evanescent wave by use of a single wavelength, there has been no method of distinguishing the unevenness of the substrate or medium surface from the recorded state, and therefore the S/N ratio is liable to be worsened, and reproducibility and stability cannot be said to be sufficient.